Certain methods and apparatus are known in the prior art for 24 hour monitoring of intraesophageal pH in patients with suspected reflux disease or other esophageal disorders. An example of a system for ambulatory 24 hour recording of gastroesophageal reflux is the Digitrapper.TM. System (manufactured by Synectics Medical AB, in Stockholm, Sweden) used with glass or Monocrystant.TM. pH catheters (as described in U.S. Pat. No. 4,119,498) and with the analysis software EsopHogram.TM. (by Gastrosoft, Inc. in Dallas, Tex.). These prior art systems typically measure pH in the esophageal tract with an intraesophageal catheter and generate reports regarding esophageal exposure of gastric juice. However, these systems measure pH values in the esophagus below 4, and do not work to detect pH values that are higher than 4.
Normally, pH values in the stomach are below 4 and in the esophagus are between 4 and 7. Hence, these prior art systems are designed to detect and measure the presence of gastric juice in the esophagus by measuring esophagus pH below 4. However, gastric juice does at times, and particularly in the early morning, become more alkaline, with a pH above 4. Hence, the prior art systems cannot detect gastroesophageal reflux of gastric juice of this type at these times, with a pH above 4.
Efforts have been made to define and report as reflux rapid changes of intraesophageal pH, while the pH remains within the normal esophageal range of pH, which is between 4 and 7. Such changes, however, can be difficult to prove to be caused by true gastroesophageal reflux, and in some instances may not be caused by reflux.
Others have measured alkaline reflux with radioisotope techniques. With these techniques, a radioisotope is administered to the patient and accumulates in the bile. With a gamma camera sensor placed externally on the patient's chest or internally within the esophagus, it is possible to detect gastroesophageal reflux containing the isotope, regardless of pH. The use of radioactive material and the expense of stationary or ambulatory gamma cameras make the radioisotope method for detection of alkaline reflux unattractive.
Intestinal impedance measurement has previously been used in measurements of gastric emptying into the intestines. In such studies, a liquid or solid meal is administered to a patient and changes in intestinal impedance are monitored from external electrodes around the abdomen. However, the prior art has not taught a system for analyzing gastroesophageal reflux by means of recording changes in esophageal impedance, nor of a system for ambulatory measurement of the same.
Impedance measurements have also been used for monitoring chest movements as a means of monitoring respiration in patients at risk for apnea. Other impedance monitors are used to detect urine leakage in the urethra in urodynamic procedures. Yet other impedance monitors are used for measurement of body fat and for phletysmography.
However, the prior art does not teach using changes in impedance for detection of gastroesophageal reflux, on an ambulatory basis or otherwise.
Since the prior art does not teach how to record and analyze alkaline reflux, it is not surprising that it also does not teach how to distinguish detection of alkaline reflux from detection of swallowed saliva. This is a matter of importance, since alkaline reflux may have a pH and an impedance that is similar to swallowed saliva, which is commonly found in any esophagus.
It is an object with the present invention to provide an ambulatory system that provides the possibility to detect gastroesophageal reflux regardless of its pH value by means of recording and analyzing esophageal impedance. It is a further object with the present invention to provide a system that can detect the direction of flow of matter in the esophagus, thus being able to separate alkaline gastroesophageal reflux from swallowed saliva. It is yet a further object of the present invention to provide presently used intraesophageal pH and pressure catheters with the means to detect gastroesophageal reflux according to the present invention. It is yet a further object with the present invention to provide a system that can be used noninvasively with a number of sensors for impedance measurements placed on and around the chest of the patient for ambulatory recording of reflux.